Conveyor chains are frequently used for moving workpieces, finished goods, and other materials through processing and handling stations in manufacturing plants, warehouses, and the like. These chains are typically heavy duty assemblies of a plurality of individual links, which in many instances are joined together by pins. Chains are also used in a variety of other industrial applications for lifting, dragging and securing; and, while this invention is described herein with reference to its use for monitoring conveyor chains, it is to be understood that it may likewise be used in connection with other types of chains.
The unexpected failure of a chain can have serious consequences in terms of safety and cost. In addition to harming personnel, failure of a chain can damage goods and equipment. Also, significant costs can occur as a result of the unanticipated downtime. In view of the foregoing, industry typically monitors the integrity and wear state of conveyor, and other, chains on a regular basis. In many instances, mechanical or electromechanical systems, non-destructive testing methods (NDT) and proof loading are used to monitor chain wear. In most instances, these systems operate to measure the length of a preselected section of a chain, since chains will generally elongate as a result of wear of their component links and connecting pins. When a predetermined amount of elongation has occurred, the chain will be taken out of service for replacement or maintenance. Some prior art chain monitoring systems are shown in U.S. Pat. Nos. 7,540,374; 5,291,131; 5,482,154; 6,851,546; 5,490,590; 5,563,392; and published U.S. Application US 2007/0056379.
Elongation of a chain may, in some instances, be caused by the collective wear of its individual links and/or pins. In other instances, elongation may be caused by the cracking or stretching of one or more individual links. In yet other instances, chain elongation may be a combination of both of the foregoing. One problem with prior art chain monitoring systems is that they operate to provide an indication of overall chain lengthening and do not address the state of individual links, and hence cannot distinguish between lengthening resultant from overall wear and lengthening resultant from individual link failure. As will be explained in detail hereinbelow, the present invention provides a relatively simple chain monitoring system which is capable of providing data indicative of chain lengthening resultant from collective wear as well as from individual link failure.